This invention relates to the immunization of equines against Streptococcus equi. S. equi causes strangles, an acute upper respiratory tract disease of horses, characterized by fever, nasal discharge and abscess formation in the retropharyngeal and mandibular lymph nodes. Horses that have been so infected in the field or experimentally infected with strangles and which do recover from strangles become highly resistant to reinfection. Moreover, only one antigenic type of S. equi has been observed in the field.
The above notwithstanding, vaccines prepared from bacterins of S. equi, or fractional extracts of the same, such as M protein-rich extracts, have been relatively ineffective to provide protection against S. equi in the field. This is true even though as far back as 1943 an article entitled "Studies with Equine Streptococcus" published in the Australian Veterinary Journal at 19: 62 by P. O. Bazeley, presented a broad-range study of the problem coupled with test results which Dr. Bazeley and other characterized as very hopeful. However, many years have passed without an adequate or effective method or means for protection of equines against strangles. One of the problems with earlier experimentation in the field was that scientists and researchers equated protection of the horse against S. equi with stimulation of bactericidal antibodies in the blood serum of the horse. In fact, vaccine failure was not due to failure of vaccines to stimulate bactericidal antibody in the serum, which it was shown did not equate with protection against field or experimental exposure to S. equi. In fact, it was discovered that ponies recently recovered from experimentally induced strangles were highly resistant to reinfection before serum bactericidal activity could be detected. Moreover, it was determined that the nasopharyngeal mucus of resistant ponies contained major IgG and IgA antibody activity against only one acid extract protein of about 41,000 molecular weight (mw), whereas serum antibodies had a number of major specificities. These findings suggested that successful vaccination requires stimulation of the nasopharyngeal immune response.
The following publications have been made by the inventor herein relating to this development:
1) Abstract No. 172 appearing Abstracts IXth, Lancefield International Symposium on Streptococci and Streptococcal Diseases, Fuji, Japan, Sep. 10, 1984; PA0 2) Infection and Immunity, March 1985, Vol. 47, No. 3, pages 623-628; PA0 3) Infection and Immunity, April 1985, Vol. 48, No. 1, pages 29-34.